Vehicle occupant restraint systems of the type having a confinement expandable from a collapsed nonoperative position to an inflated operative position require a source of inflating fluid which must respond to a collision signal within a short duration of time, typically 50 milliseconds or less. Where it is desired to provide such an occupant restraint for the vehicle driver, it has been found desiable to provide the source of inflating fluid as a compact integral unit within the collapsed confinement. In order to provide crash restraint for the vehicle operator, it has been found desirable to mount the inflatable confinement on the hub of the vehicle steering wheel. In order to provide the compact unit of confinement and inflator in a form low in weight and rotary inertia for steering wheel mounting, it has been found desirable to utilize an inflator having gas generating means for providing a portion of the inflating fluid.
Inflators for vehicle occupant restraints having gas generating means typically utilize ignitable and combustible solid chemical mixtures which require the combustion products thereof to be filtered, trapped and diffused before entry into the confinement for inflation. As mentioned above, it is desirable that the inflator assembly be low in transverse profile for compact mounting on the steering wheel hub, and therefore, a minimum extension in a direction axially of the steering column. Furthermore it is desirable that the exit ports of the diffuser provide reactionless flow from the inflator in the event that the inflator is inadvertently activated during manufacture, shipping or assembly onto the vehicle. Therefore, it has been found desirable to dispose the diffuser exit ports in a circumferentially equally spaced radial-flow arrangement.
Where the inflator for the inflatable confinement is of the hybrid type having reservoir means containing gas generating means in addition to pressurized stored fluid, it has been found convenient and desirable to have the reservoir shaped to an annular configuration for steering wheel mounting with the gas generating means disposed within the central region of the reservoir. One configuration which has been found satisfactory for the combination, or hybrid, inflator is an inflator having an axial outlet passage with respect to the annular reservoir, with the diffuser disposed over the axial outlet passage. However, in such an arrangement, the diffuser adds additional axial length to the inflator causing the assembly to extend an undesirable distance in a direction toward the occupant when the inflator is mounted on the steering wheel. Therefore, it has been desired to provide a diffuser for a steering wheel mounted inflator for an inflatable occupant restraint wherein the inflator assembly including the diffuser, has the lowest possible profile in a direction axially of the steering column.